Analysis of Durability of Advanced Cementitious Materials for Rigid Pavement Construction in California

The cementitious materials under consideration by Caltrans for rigid pavement construction may be classified into four categories: Portland cements and blends, calcium aluminate cements and blends, calcium sulfoaluminate cements, and fly ash-based cements. With the exception of Portland cements, most of the cementitious materials under consideration have not been extensively used for pavement construction in the United States, and little information about their long-term durability is available. If rigid pavements are to achieve the 30+ year service life defined by Caltrans, it is essential to characterize the long-term resistance of the concrete to sulfate attack, aggregate reactions, corrosion, and freeze-thaw action. California soils are known to be rich in sulfates. Sulfate resistance of concrete is largely determined by the permeability of the concrete and by the reactivity of the hydration products present. Sulfates may permeate concrete and react with existing hydration products to form ettringite or gypsum. Hydrated cement paste containing larger proportions of monosulfate hydrate, calcium aluminate hydrate, or calcium hydroxide is more vulnerable to damage by sulfate attack. Because they contain greater proportions of these hydration products, certain types of Portland cements are particularly susceptible to sulfate attack. In general, low permeability concrete produced from sulfate-resistant Portland cements, Portland-pozzolan blends, calcium aluminate cements and blends, calcium sulfoaluminate cements, and fly ash-based cements are expected to exhibit improved performance in sulfate-rich environments. However, the chemical composition of several cements submitted for consideration by Caltrans have not been provided by the manufacturers. Thus, ongoing accelerated sulfate testing is being performed to measure the potential long-term durability of each 2 cement in aggressive sulfate environments. A description of the accelerated test program is included in this report. Two forms of aggregate reactions known to occur in California are addressed: alkali-aggregate reaction and oxidation reactions. The alkali aggregate reaction is greatly dependent upon the alkali content of the cement. Clays used in the manufacture of Portland cements may contribute high alkali concentrations to the pore solution. Low-alkali Portland cements may be specified when needed to provide resistance to alkali-aggregate reactions. Portland-pozzolan blends and calcium aluminate cements and blends are expected to exhibit improved alkali-aggregate reaction resistance in sulfate-rich environments, while the resistance of calcium sulfoaluminate cements is expected to be similar to that of Portland cement. Fly ash-based cements may exhibit improved resistance, but the alkali concentration contributed by the set accelerator should be investigated. The oxidation of sulfide and sulfate minerals, …